A search conducted in the U.S. Patent Office resulted in the citation of the following patents: U.S. Pat. Nos. 2,956,865; 3,180,712; 3,503,715; 4,118,199; 4,225,561; German Nos. 2,452,717; 2,555,038; 2,628,439; and Japanese No. 1978-3962.
U.S. Pat. No. 2,956,865 discloses a rather complex apparatus for purifying exhaust gases. The structure includes elements which are adapted to add additional fuel to the exhaust gases and structure in which the exhaust gases and additional fuel are burned.
U.S. Pat. No. 3,180,712 discloses a two-stage converter muffler structure. This device has two different catalyst beds which are separated by structure through which auxiliary air may be added to the converter.
U.S. Pat. No. 3,503,715 is directed to an apparatus for treating an exhaust gas stream with different catalyst beds. One catalyst layer comprises platinized alumina particles and the next adjacent layer comprises platinized alumina particles containing a barium, calcium or strontium component.
U.S. Pat. No. 4,118,199 is directed to a monolithic carrier catalyst and arrangements of such a catalyst for the purification of exhaust gases from an internal combustion engine. The structure taught is one in which an increased concentration of catalytically active material is found on the monolithic catalyst carrier. The concentration of the catalytic component increases in the direction of flow of the exhaust gases.
U.S. Pat. No. 4,225,561 is directed to a catalytic converter for transforming gases from one condition to another. The structure disclosed is a rather complex one involving inner and outer canning structure members and means for supporting the same.
German No. 2,452,717 is directed to a catalytic engine exhaust gas treatment system. The system is characterized in that the exhaust gases are first passed through an oxidation catalyst to oxidize part of their hydrocarbons and carbon monoxide content and to reduce their oxygen content to a predetermined amount. Thereafter, the exhaust gases are passed over a reducing catalyst where the nitrogen oxides are reduced. A final catalytic oxidation stage then follows to oxidize any remaining hydrocarbons and carbon monoxide.
German No. 2,555,038 is also directed to a catalytic converter for use with an internal combustion engine. This device includes a twin type structure in which the exhaust gas purifier has a noble metal section followed in the same housing by a non-noble metal section.
German No. 2,628,439 is directed to a catalytic converter structure. The catalytic converter contains a silver or palladium plated grid, the inner parts of which permit expansion in the chamber and absorption of energy of the sound pressure waves in the exhaust gas by forming an artificial turbulence in the gas stream.
Japanese No. 1978-3962 is directed to a catalytic gas purifier for use with internal combustion engines. A primary catalytic unit is used along with an auxiliary catalyst unit which is disposed upstream of the primary catalytic unit.
We are also aware of teachings contained in commonly assigned U.S. patent applications Ser. No. 284,759, now abandoned, entitled "Palladium Catalyst Promoted by Tungsten"; Ser. No. 284,762, now U.S. Pat. No. 4,374,103, entitled "Low Cost Catalyst System"; and Ser. No. 284,763, now U.S. Pat. No. 4,389,382, entitled "Simplified Low Cost Catalyst System", all filed on July 20, 1981.
The Ser. No. 284,759 application teaches a specific catalyst system in which a palladium catalyst is promoted by tungsten. The catalyst system disclosed in that application has highly desirable characteristics in that it is effective in the catalytic oxidation of unburned hydrocarbons and the catalytic reduction of oxides of nitrogen without significant production of ammonia when an internal combustion engine with which it is associated is operated under fuel rich (oxygen deficient) conditions.
The Ser. No. 284,762 catalyst system disclosed is one which teaches a catalyst formulation in which a catalyst substrate is provided with both an upstream catalyst portion and a downstream catalyst portion. The upstream and downstream catalyst portions contain palladium while the downstream catalyst portion additionally contains tungsten.
In the Ser. No. 284,763 application the catalyst formulation is also found on a suitable catalyst substrate having both an upstream catalyst portion and a downstream catalyst portion. The upstream catalyst portion contains finely divided palladium thereon while the downstream portion contains only tungsten thereon.